No matter your poison -- coffee, tea, hot chocolate, sake -- take a gulp too soon out of the pot and chances are good that you'll burn your mouth. But build this Smart Coaster and you'll always know when it's safe to sip.

According to my thermometer, common coffee brewers produce a cup of perfect coffee that is positively molten to the tongue, at 160ºF. Even as this marvelous beverage fills your room-temperature cup, temps can still reach a blistering 137.1ºF. Finally, after a couple of minutes cooling, your coffee is safe to drink, at a lukewarm 116.5ºF.